[AK4186]
OPERATION OVERVIEW
■
Function Overview
The AK4186 consists of the following blocks:
●
1.6V Successive Approximation Resister (SAR) A/D converter
●
4-wire or 5-wire resistive touch screen controller interface
●
Single or Continuous A/D conversion
●
Internal Clock for SAR A/D Converter
●
I
2
C
TM
I/F
■
A/D Converter for Touch Screen
The AK4186 integrates a 12bit successive approximation resistor (SAR) A/D converter for position measurement,
temperature, and auxiliary input. The architecture is based on capacitive redistribution algorithm, and an internal
capacitor array functions as the sample/hold (S/H) circuit.
The SAR A/D converter output is a straight binary format as shown below:
Input Voltage
Output Code
FFFH
(ΔVREF-1.5LSB)~
ΔVREF
FFEH
(ΔVREF-2.5LSB) ~ (ΔVREF-1.5LSB)
---------
---------
0.5LSB ~ 1.5LSB
001H
0 ~ 0.5LSB
000H
ΔVREF:
(VREF+) – (VREF-)
Table 1. Output Code
The f
OSC
clock of an internal oscillator is used for A/D conversion. The full scale (ΔVREF) of the A/D converter
depends on the input mode. Position and pen pressure are measured in differential mode, and then IN is measured in
single-ended mode. The AK4186 is controlled by 8bit serial command. A/D conversion result is 12bit data output on
the SDA pin.
■
Analog Inputs
The analog input channel is automatically selected in sequential measurement mode. When position detection (X-axis
and Y-axis) and pen pressure are selected as analog inputs in differential mode, the full scale (ΔVREF) is the voltage
difference between the non-inverting terminal and the inverting terminal of the measured axis (e.g. X-axis
measurement: (XP) – (XN)). Analog input to A/D converters (ΔAIN) is the voltage difference between the non-
inverting terminal of the non-measured axis and the inverting terminal of the measured axis. At single-ended mode, the
full scale of A/D converter (ΔVREF) is the voltage difference between the VDD and the VSS. The analog input of A/D
converter (ΔAIN) is the voltage difference between the selected channel (IN) and the VSS.
If the source of analog input is high impedance, longer tracking time is required. Then A/D conversion should be started.
Status of Driver Switch
X-Driver
Y-Driver
OFF
OFF
ON
OFF
OFF
ON
XN-ON
YP-ON
XN-ON
YP-ON
ADC input (ΔAIN)
AIN+
AIN-
IN
GND
YP
XN
XP
YN
XP
XN
YN
XN
Reference Voltage (ΔVREF)
VREF+
VREF-
VREF
GND
XP
XN
YP
YN
YP
XN
YP
XN
Channel Selection
AIN Measure
X-axis Measure
Y-axis Measure
Z1 Measure (Pressure)
Z2 Measure (Pressure)
Ref. Mode
SER
DFR
DFR
DFR
DFR
Table 2. Measurement Mode (4-wire)
MS1068-E-04
-7-
2011/03
AKM [ ASAHI KASEI MICROSYSTEMS ]
